Challenges video games controller designers may have is hand size because not everyone will have the same hand size. Controller designers want their controller to appeal to as many people as possible so they have to make it a controller a good and comfortable size for all hand sizes. Hand size is also relevant for where they place the buttons, designers will want all or most of the buttons in reach without having to move your hands from a fixed position. Now most controllers are similar and the reason for this may be that controller designers may have found the most optimal controller that appeals to every person who plays with a controller.
I have a PS3 and Xbox 360 and I would have to say that my favorite controller is the Xbox 360 controller because it fits the best in my hand and I think the placement of the buttons and analog sticks are placed in a way the is comfortable and I can play for a long time having my hands stay comfortable the whole time.